Fix 3D length shorter than 2D length

- [x] add all original points when draping
- [ ] find a way to recompute all 3d geoms
- [ ] add tests about length
- [x] update changelog
Of course this will increase the number of points. But this does not really get rid of sampling.

Anyway I think the 3D geom should preserve the 2D geometry and should not take shortcuts in sharp turns so we have to keep all original points and add new points only in between.

A better (but more complex) solution is to sample on each segment rather than the whole linestring.